This project studied the responses of trigeminothalamic neurons responding to noxious and innocuous mechanical and thermal stimuli in both anesthetized and awake, behaving rhesus monkeys. Studies in the anesthetized monkey yielded data on 3 classes of neurons capable of transmitting information about noxious stimuli. Two classes tended to be specifically adapted to convey noxious information. A third class responded differentially both to innocuous and noxious stimuli. Studies of trigeminothalamic neurons in the awake, performing monkey have, to date, provided information on 3 classes of neurons responding to noxious and innocuous thermal stimuli. Nociceptive neurons often had thresholds below 40 degrees C, but stimulus response functions were positively-accelerating in the noxious heat range. The response properties of a second class of cells, phasic polysensory neurons, may signal the presence of behaviorally significant thermal and visual stimuli. Conversely, the activity of tonic polysensory neurons may be associated with the execution of motor behaviors evoked by salient sensory stimuli. BIBLIOGRAPHIC REFERENCES: Dubner, R., Gobel, S., and Price, D.D.: Peripheral and central trigeminal pain pathways. In: Bonica, J.J. and Albe-Fessard, D. (Eds.): Advances in Pain Research and Therapy, Vol. I, Raven Press, New York, 1976, pp. 137-148. Price, D.D., Dubner, R. and Hu, J.W.: Trigeminothalamic neurons in nucleus caudalis responsive to tactile, thermal and nociceptive stimulation of monkey's face. J. Neurophysiol. 39: 936-953, 1976.